IC Engine -Cycle Analysis
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Transcript of IC Engine -Cycle Analysis
8/12/2019 IC Engine -Cycle Analysis
http://slidepdf.com/reader/full/ic-engine-cycle-analysis 1/26
8/12/2019 IC Engine -Cycle Analysis
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Approaches Air-Standard cycle analysis
Fuel-Air cycle analysis
Actual cycle analysis
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Basic Thermodynamic Cycles
Otto Cycle
Diesel Cycle
Dual Combustion Cycle
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Air-Standard cycle analysis to perform elementary analyses of IC
engine cycles
simplifications include: fixed amount of air (ideal gas) for working
fluid
combustion process not considered
intake and exhaust processes not considered
engine friction and heat losses not considered
specific heats independent of temperature
all processes are reversible
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Otto Cycle
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Diesel Cycle
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Dual Combustion Cycle
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Comparison of cyclesSame Compression ratio & Heat addition
diesl dual otto
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Comparison of cyclesSame Max.pressure & Heat addition
ott dual diesel
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Fuel-Air Cycles: Significancefactors taken into account actual composition of cylinder gases
variation of specific heat w.r.ttemperature
effect of dissociation
variation in the no of moleculesAnalysis gives effect of variation ofF/A ratio and compression ratio
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Fuel-Air Cycles : assumptions no chemical change in fuel/air prior to
combustion
charge is in chemical equilibrium
compression and expansion are adiabatic &frictionless
fluid motion inside cylinder is ignored
fuel is completely vaporized and perfectlymixed with air (for Otto cycle)
burning takes place instantaneously (forOtto cycle)
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Fuel air cycle- Otto
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Fuel air cycle- Diesel
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Composition of Cylinder gases A/F ratio changes during engine
operation
Thus affects composition of gasesbefore & after combustion Amount of exhaust gases in clearance
varies with load
Analysis which includes this, needsnumerical techniques (computeranalysis)
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Variable Specific heats p-V
diagram
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Effect of dissociation on Temp
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Dissociation in p-V diagram
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Actual CyclesOTTO DIESEL
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Reasons for the deviation Mixing of A/F mixture with products of
combustion from the previous cycle
Change in chemical composition of mixture
Variation of specific heats with temperature
Gas leakage, fluid friction
Not instantaneous combustion
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Loss of power in Actual
Cycles Time loss
Heat loss
Exhaust blow down loss
Pumping loss
Friction loss
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Time loss
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Time loss Increases Loss on compression
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Time loss Decreases Loss on compression
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Heat loss, Blow down loss and
Pumping loss Heat loss during combustion and expansion
(to components, cooling medium,lubricant)
Reduces max.temp & contributes 12% Blow down loss due to early opening of
exhaust valve
contributes 2%
Pumping loss due to pumping gas fromlower inlet pressure to higher exhaustpressure
contributes 2% and increases with speed
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Effect of losses on p-v diagram
